How do you workout the optimal floorspace usage, and thus the point at which an idea is feasible?

(Clearly an RDE/FEC is going to have to tend towards having mausment arcade elements because that's a revenue source)

I'd also like to be able to know how much floorspace needs to be allocated to revenue/entertainment vs non revenue utility functions (i.e walkways/restrooms/ chutes/lifts employee facilites which parks have but which you don't see.)

If I can borrow some Disney terminology, there's "off stage" and "on stage" (guest) areas.

It's very simple: When you're designing the space, you want to have the least amount of "off stage" areas as possible. You don't want to pay for building space that is not generating revenue. If you can make it zero, you absolutely should. But of course employees need restrooms, breakrooms, offices, stock rooms etc... but in an ideal world, that number is zero. Bottom line: Make it as small as you can while still being functional.